1. Field of the Invention
This invention relates to medicinal dressings that provide an advanced healing environment for wounds. Good wound healing is characterized by rapid and complete regeneration of the damaged tissue. Considerable efforts have been expended in the study of wound dressings with the aims of finding which dressings are most effective in promoting wound healing. The process of wound healing is complex and is not fully understood. High macrophage activity is desirable, particularly during the early stages of healing, to kill bacteria and to remove cell debris and foreign matter. This activity is generally accompanied by inflammation. High fibroblast activity is desirable, particularly during the later stages of healing, to produce a high rate of regeneration.
Enhanced concentrations of active free radicals are often found in wounds, in particular small oxygen-containing free radicals such as the hydroxyl radical (OH.), the hydroperoxyl radical (OOH.) and the superoxide anion (O.sub.2.sup.-). The latter two are in protonation equilibrium, with the anion predominating at physiological pH; the hydroperoxyl radical is a more active free radical than the superoxide anion. The presence of these radicals is believed to be advantageous in the early stages of healing, attracting macrophages into the wound and promoting the respiratory burst. Their continued presence is, however, believed to be detrimental. They are thought to promote continued inflammation and so to delay healing and in severe cases to induce tissue necrosis and permanent tissue damage. In contrast, oxidizing species without unpaired electrons, such as hydrogen peroxide (H.sub.2 O.sub.2), are believed to be considerably less harmful.
2. Description of the Related Art
The process of wound healing consists of three phases during which the injured tissue is repaired, regenerated, and new tissue is reorganized into a scar. These three phases are classified as: a) an inflammation phase which begins from day 0 to 3 days, b) a cellular proliferation phase from 3 to 12 days, and c) a remodeling phase from 3 days to about 6 months. In all three phases, antioxidants play a vital role in the healing process.
In the inflammation phase, inflammatory cells, mostly neutrophils, enter the site of the wound followed by lymphocytes, monocytes, and later macrophages. The neutrophils that are stimulated begin to release proteases and reactive oxygen species into the surrounding medium with potential adverse effects on both the adjacent tissues and the invading microorganisms. The oxygen species known to be released by the neutrophils are superoxide (O.sub.2.sup.-) through the action of a plasma membrane-bound NADPH oxidase, hydrogen peroxide (H.sub.2 O.sub.2) formed by action of dismutation of O.sub.2.sup.-, and HOCl produced by the action of myeloperoxidase with H.sub.2 O.sub.2.
The proliferative phase consists of laying down new granulation tissue, and the formation of new blood vessels in the injured area. The fibroblasts, endothelial cells, and epithelial cells migrate in the wound site. These fibroblasts produce the collagen that is necessary for wound repair. Ascorbic acid is crucial in the formation of collagen. Several studies have demonstrated that ascorbic acid was capable of overcoming the reduced proliferative capacity of elderly dermal fibroblasts, as well as increasing collagen synthesis in elderly cells by similar degrees as in newborn cells even though the basal levels of collagen synthesis are age dependent A decrease of ascorbic acid at the injury area will decrease the rate of wound healing.
In reepithelialization, epithelial cells migrate from the free edges of the tissue across the wound. This event is succeeded by the proliferation of epithelial cells at the periphery of the wound. Research has also shown that reepithelialization is enhanced by the presence of occlusive wound dressings which maintain a moisture barrer.
The final phase of wound healing, which is remodeling, is effected by both the replacement of granulation tissue with collagen and elastin fibers and the devascularization of the granulation tissue. Recent studies have shown that topical application of antioxidants, especially alpha-tocopherol, reduces scarring and normalizes blood coagulation during therapy.
As described in U.S. Pat. No. 3,812,252, a particularly effective healing treatment for wounds and skin defects such as bums, ulcers and lesions is the application of a medicinal dressing containing as an essential ingredient starch hydrolysate having Dextrose Equivalent of less than about 35. In such wound treatment the starch hydrolysate produces the formation of a film which is intimately adhered to the underlying granulation tissue and which is semi-permeable to gas and fluids and provides an ideal protective cover that will reduce fluid and plasma losses and invasion by pathogenic bacteria. In addition, it appears that the starch hydrolysate provides a topical or local hyperalimentation, that is local nutrition, providing a gradual release of glucose which is particularly effective in nutrition of tissue, both damaged and nascent, which have become relatively isolated from normal blood flow nutrition. The cessation of blood flow to such an ischemic lesion can be developed in a slow and gradual form such as in the case of decubitus ulcers and stasis ulcers, or may take place more acutely such as in thermo-radiation and chemical burns. In the absence of nutrition, the rate of fluid delivery of nutrients decreases bringing a progressive impairment in the viability of cells and tissues. This eventually leads to degeneration and death of the tissue and cells in a condition known as necrosis. Necrosis is generally accompanied by bacterial, fungal and/or viral contamination. As further pointed out in the aforementioned patent, treatment of exudative skin wounds with a starch hydrolysate dressing produces a greatly reduced bacteria count of an infected wound and inhibits infection of an uninfected wound. In addition, application of the starch hydrolysate to a wound or ulcer produces a film or semi-permeable membrane which allows edematous liquid to pass through while proteinaceous material is retained within the body, allowing reduction in the volume of exudate in relatively clean condition.
U.S. Pat. No. 4,837,024 describes compositions which enhance and promote the wound healing process and which comprise suspensions of the fibrous protein, collagen, and of a polysaccharide, namely a glycosaminoglycan. The glycosaminoglycan is one which exhibits chemotaxis for fibroblasts or endothelial cells; the preferred glycosaminoglycans are said to be heparin, heparan sulfate and alginate, although it should be noted that alginate is not in fact a glycosaminoglycan.
The compositions of the present invention include collagen type I, vitamins such as ascorbic acid (vitamin C) and alpha-tocopherol (vitamin E), and particulate starch hydrolysate that are applied on wounds to promote the formation and growth of healthy granulation tissue. The repair process for even minor breaches or ruptures takes a period of time extending from hours and days to weeks; and in some instances, as in ulceration, the breach or rupture may persist for extended periods of time, i.e., months or even years. At all times, be it brief or extended, the potential for invasion by pathogenic organisms or foreign substances continues until new tissue has been generated to fully close the rupture or breach. Because of the danger of infections, the customary management of wounds includes an initial thorough cleansing of the affected area to remove any contaminants such as dirt, cloth particles, or other debris that may introduce pathogenic materials. Any hopelessly damaged tissues may be debrided and antiseptic materials are applied to make the area as sterile as possible. If considered necessary, sutures may be used to reduce the area of the underlying tissues and thereby limit the amount of tissue exposed to subsequent contamination.
The healing process is brought about by complex biological mechanisms generally involving several groups of special cells and proteins. Leukocytes, such as neutrophils and macrophages, crown the wound site and digest foreign pathogens and debris. Such cells also send out chemical signals that marshal fibroblasts in the wound vicinity and ultimately generate connective structures, principally, collagen, which make up a major portion of the new tissues. Endothelial cells generate new blood capillaries that grow into the reconstructed tissue areas where their presence is necessary to supply nutrients to the newly growing tissue cells and remove catabolic products. As the new capillaries grow, the cells on the margin of the wound simultaneously multiply and grow inwardly. The fibrous tissue arising from this cell growth eventually fills the wound cavity with a network of interlacing threads of collagen which in due time, arrange themselves in firm bands and form the permanent new tissue.
The surface of the wound is subsequently covered by processes of enlargement, flattening, and multiplication of the epithelial cells at the wounds' edge. These epithelial cells spread as sheets into the wound, beneath the scab. Eventually the proliferating epithelial cell sheets emanating from the wound sides coalesce to cover and close the wound on the outer surface. Until such time as at least superficial healing has occurred, or healing is impaired, the individual remains at risk from continued or new infection. Hence, there is a time versus rate related risk factor involved in all wound situations. The quicker the wound can heal, the sooner the risk is removed. Therefore, any procedure that can influence the rate of wound healing, or even favorably influence the healing of intractable wounds, would be of paramount value.
In accordance with this invention, improvements in the starch hydrolysate treatment of wounds have been developed to provide dressing for wound treatment, effective to promote the healing process, as well as beneficial compounding of the starch hydrolysate material.